1. Field of the Invention
The present invention relates to a disk array device and a channel adapter.
2. Description of the Related Art
A disk array device is a large-capacity storage control device where plural storage disks are disposed in an array and which is constructed on the basis of, for example, RAID (Redundant Array of Independent Inexpensive Disks). For example, hard disk devices and semiconductor memory devices are used as storage devices. A logical volume is formed on a physical storage region that each storage device provides. A host computer such as a business-use server issues a predetermined command, whereby the host computer can read data from the logical volumes and write data to the logical volumes.
A disk array device configuring part of a SAN (Storage Area Network) conducts data transfer in block units in accordance with a fibre channel protocol. A SAN according to a fibre channel is called an FC-SAN. In an FC-SAN, high-speed data transfer can be conducted using a fiber-optic cable or a metal cable. Also, by using a fibre channel switch, a fabric structure can be obtained, and numerous disk array devices and numerous host computers can be interconnected.
One viewpoint of improving the reliability of disk array devices is whether or not the transmission and reception of data can be accurately conducted. For this reason, technology such as an LRC (Longitudinal Redundancy Check), a CRC (Cyclic Redundancy Check) and an ECC (Error-Correcting Code) is used in disk array devices.
Technology that checks whether or not data reception between a channel unit, which conducts data communication with a host computer, and a disk interface control board, which conducts data communication with a magnetic disk, has been conducted accurately is also known (U.S. Pat. No. 5,561,672). In this technology, a data buffer and a parity check circuit are respectively disposed on three control boards: the disk interface control board, a channel interface control board and a channel unit. When data is transferred between the control boards, a parity check is respectively conducted by each control board of the sender and receiver, the storage content of the data buffer of the sender and the storage content of the data buffer of the receiver are compared, and it is determined whether or not the data has been properly transferred.
In a case where data is sent from a disk array device to a host computer in an FC (Fibre Channel)-SAN, the data is sent to the host computer as a frame including about 2 KB of block data. The frame of the fibre channel is disposed with information representing the start of the frame (SOF), frame header information, a data field, a CRC and information representing the end of the frame (EOF). 0 to 2112 bytes of data can be stored in the data field. One or more frames are sent from the disk array device to the host computer in response to a request from the host computer.
An FC-SAN is a network in which high-speed data transfer is possible and which is stable in comparison to an IP network. Thus, there is little potential for sent data to be lost during transmission and for unrecoverable errors to arise in the data received by the host computer. Due to these circumstances, an FC-SAN is configured to retransmit all sent data in a case where trouble has arisen in part of the sent data.
In recent years, broadband network systems based on TCP/IP (Transmission Control Protocol/Internet Protocol) such as the Internet and the Intranet have become widespread, and technology that improves the fusion between IP (Internet Protocol) networks and storage systems (disk array devices) has been proposed. An IP-based SAN is called an IP-SAN. Technology where an SCSI (Small Computer System Interface) command set is serialized as a TCP/IP packet and a disk array device is directly connected to an IP network is known as one mode of an IP-SAN. This technology is known as iSCSI (Internet SCSI) or SCSI over IP.
An IP network is a complex network configured from plural servers, routers and switches, and the bandwidth and degree of congestion are ever-changing. Packets sent from a sender to a receiver have no guarantee of arriving in the sent order and there are cases where all or some of the packets are lost during transmission. Thus, a TCP/IP network is configured to be able to request partial retransmission of only lost data in a case where some of the data of the series is lost or an error has occurred.
In a case where a disk array device is directly coupled to an IP network, the difference in the technical makeup between the protocol used outside the disk array device (TCP/IP) and the protocol used inside the disk array device (FC) becomes a problem. Namely, in a case where retransmission is requested by the host computer in regard to part of data inside a frame, the requested data itself can be sent but the fact that the partial data is the correct data cannot be guaranteed. In a fibre channel, because one CRC is disposed in regard to all frames, a data guarantee cannot be conducted in regard to data in a case where part of the data inside the frame is to be retransmitted.